Low-Cycle Fatigue of Ultrafine-Grained Aluminum at Low Temperatures

摘要

Ultrafine-grained (UFG) Al of 99.98~99.99% purity was fabricated by equal channel angular pressing. Fully reversed tension-compression low-cycle fatigue tests were earned out under plastic strain control at various temperatures between 83 K and 300 K. At 300 K, UFG Al showed rapid cyclic softening. As test temperature decreased, cyclic softening became less significant and at 83 K, UFG Al showed cyclic hardening till saturation. Formation of shear bands and development of dislocation structure were the characteristic features of fatigued specimens. As test temperature decreased, the area fraction of shear bands on specimen surface decreased and at 83 K, shear bands could not be observed. In addition, local grain coarsening occurred except at 83 K. Formation of dislocation cell and wall structures became more frequent at lower temperatures and well-developed dislocation walls were formed in grains as small as 1.5 um in size at 83 K.